Detection of a pulse wave is extremely important in understanding a physiological state of a human being and a technology for detecting this from a remote place in a non-contact manner is in demand.
Such technologies include a study made by Massachusetts Institute of Technology which is a non-patent literature.
This technology detects a pulse wave by taking a moving image of the face of a subject by a web camera and analyzing the moving image by a laptop computer after the photographing (that is, not by real-time processing but by processing later).
This study realizes non-contact detection of a pulse wave by using an inexpensive general purpose device and a simple method against conventional detection of the pulse wave by using a special expensive device such as a laser and Doppler radar.
Here, an outline of this technology will be described by using FIG. 16.
First, as illustrated in FIG. 16(a), an evaluation region 101 having a rectangular shape is set on a screen of the moving image, the subject is seated so that the face of the subject is contained in the evaluation region 101, and the face in a still state is photographed in a moving image. The experiment is conducted indoors, and sunlight incident through a window is used as a light source.
By separating the obtained moving image into each of an R component, a G component, and a B component and averaging them, fluctuations on which the pulse waves is superimposed are obtained as illustrated in FIG. 16(b).
Each of these components include a pulse wave signal weighted in accordance with a light absorbing characteristic of hemoglobin or the like, and the pulse wave is obtained by conducting ICA (Independent Component Analysis) or the like on it.
The pulse wave is obtained from the moving image as above because, since a volume of a blood vessel is changed in accordance with heartbeats of the subject, an optical distance that the sunlight is transmitted through the skin is changed, and it appears as a change in reflected light from the face.
However, this technology is performed under an ideal environment of a laboratory, and there has been a problem that use in a practical scene such as detection of the pulse wave of a driver by mounting a pulse wave detection device on a vehicle is difficult due to various disturbance elements.
If a target of pulse wave detection moves, for example, the face of the target goes out of the evaluation region 101, whereby the pulse wave cannot be detected any longer.
Moreover, since a background 102 outside the face and a region where the pulse wave cannot be detected such as hair, eyes, eyebrows, mouth and the like are also included in the evaluation region 101, there is also a problem that detection accuracy lowers.